1. Field of the Invention
The present invention relates to a roller driven by its own built-in electric motor. Herein, this type of roller will be called xe2x80x9cmotorized rollerxe2x80x9d.
2. Description of Related Art
The motorized rollers are in wide use in conveyors for transporting commodity and products. The motorized roller usually incorporates a speed reducer, and the typical examples are disclosed in Japanese Laid-open Patent Applications Nos. Hei 11-79358, Hei 8-188219, Hei 8-2643, Hei 7-279998, and Hei 6-227630.
The known motorized rollers use an induction motor. In recent years, in order to meet the general demand for more precise control, it is common that the motorized rollers use brushless motors.
The main advantages of a brushless motor are the omission of a brush or communicator, the attainment of a constant output for the same conditions, and the operational efficiency.
On the other hand, the brushless motor has disadvantages that it requires a pole detector which needs lead wires in addition to the power cable, and a complicated motor driver circuit board must be equipped to control a current supplied to the brushless motor, the circuit board being mounted on the body of the motorized roller, and the lead wires from the roller being connected to the circuit board. The external wiring is a troublesome work. An example is disclosed in Japanese Laid-open Patent Application No. Hei 8-91532.
Therefore, the known motorized roller using a brushless motor is practically disadvantageous in that the consumption of time and toil is involved in electrical connection when the motorized roller is incorporated in machines such as conveyors, and the wiring tends to become twisted in an untidy state. In addition, the repair of the motorized roller consumes time and toil.
The present invention is directed to solve the problems pointed out above, and has for its object to provide a motorized roller which ensures easy wiring connection and ready installing into other machines such as conveyors.
Another object of the present invention is to provide a motorized roller capable of releasing heat which otherwise would be likely to build up in the roller body and damage the component parts therein.
According to one aspect of the present invention, the motorized roller includes a roller body, an electric motor, a speed reducer, and an electronic device accommodated or housed within the roller body to control a current supplied to the motor, wherein the roller body accommodates the electric motor and the speed reducer, and is rotated by the electric motor through the speed reducer.
According to another aspect of the present invention, the motorized roller includes a roller body, an inner shell, an electric motor, a speed reducer, and an electronic device housed within the inner shell to control a current supplied to the motor, wherein the inner shell accommodates the electric motor and the speed reducer, and the roller body is rotated by the electric motor through the speed reducer.
According to a further aspect of the present invention, the motorized roller has a roller unit which includes a casing, a fixed shaft protruding from the casing, a driving portion provided within the casing, an electronic device housed within the casing, and a rotating member having a larger diameter than the casing, wherein the driving portion includes an electric motor, the electronic device is adapted to control a current supplied to the motor, and the rotating member is rotatable upon reception of a force from the driving portion. When the casing is inserted in an external roller separately prepared, the fixed shaft protrudes from the external roller and the rotating member engages with an inner surface of the external roller to rotate the external roller.
Preferably, the motorized roller includes a heat releaser housed within the roller body, wherein the heat releaser directly or indirectly contacts the electronic device so as to allow heat generating in and around the electronic device to dissipate.
Preferably, the electronic device incorporated in the motorized roller of the present invention is a transistor to control a current supplied to the motor but as a result of the amplification of a current through the transistor, heat generates, and builds up in the roller body. The heat is likely to damage the components, and lead to loss of control. Therefore, the dissipation of heat is essential for smoothly operating the motorized roller.
It is preferred that thermally conductive grease is applied between the heat releaser and the electronic device to facilitate heat transfer between them.
The heat releaser and the electronic device may be separated by a suitable electrical insulator, which hereafter will be referred to as xe2x80x9cinsulatorxe2x80x9d.
According to a further aspect of the present invention, an inner shell is provided in the roller body to accommodate the electronic device and a heat releaser, such as through radiation and conduction, which is directly or indirectly kept in contact with the inner shell and the electronic device. The heat releaser housed inside the inner shell together with the electronic device works as a heat radiator for dissipating heat generating in and around the electronic device. In this case, the inner shell also radiates and dissipates heat and works as a part of the heat radiator, whereas the heat releaser works also as a heat conductor. Preferably, the area of the outer surface of the inner shell is larger than that of the heat releaser so as to facilitate heat dissipation. Thus the electronic device and others are protected from being damaged by heat. The inner shell is fixed with respect to the ground or floor; if it inadvertently rotates, undesired friction occurs between the heat releaser and the inner shell.
Preferably, the heat releaser has a curved outer surface conforming to the inner surface of the inner shell so as to prevent any gap from occurring therebetween and reducing the efficiency of heat transfer.
The electronic device can be housed in a container, for example, made of plastics, and the container is housed within the roller body together with the heat releaser, which is exposed to both inside and outside the container to prevent heat buildup in the container. The container is preferably provided with an opening such as an aperture or cutout into which the heat releaser is inserted.
Preferably, the fixed shaft has an internal bore through which a cable for supplying electrical current to the motor in the driving portion runs. Such a structure can be employed when main components are housed in a unit.